EP2349637A1 - Method for manufacturing a hollow body of zinc plated sheet metal for an automobile - Google Patents

Abstract

The invention relates to a method for manufacturing a hollow body (10) of zinc plated sheet metal comprising at least one first sheet metal panel (12) assembled to a second sheet metal panel (14), said first panel (12) comprising a main portion (18) perpendicular to a parallel end portion (18), connected by a radius of curvature (20), said method comprising at least one laser welding step during which the first panel (12) is laser welded to the second panel (14) with a predetermined clearance (J), characterised in that the invention comprises at least one prior positioning step during which the panels (12, 14) are placed one on top of the another with no clearance, and in that during the laser welding step, the laser beam (27) is positioned in an area of the radius of curvature (20) of the first panel (12) corresponding to the predetermined clearance (J) between the first and second panels (12, 14), for “transparency” welding.

Description

 Process for manufacturing a zinc-plated hollow body for a motor vehicle

The invention relates to a method for manufacturing a hollow body of galvanized sheet for a motor vehicle.

The invention relates more particularly to a method of manufacturing a zinc-plated hollow body for a motor vehicle, said hollow body comprising at least a first sheet metal panel assembled to a second sheet metal panel, said first sheet metal panel comprising at least a main portion perpendicular to the second panel, an end portion parallel to the second panel and a defined radius of curvature connecting said end portion to the main portion, said method comprising at least one soldering step in which the first panel is laser welded to the second panel respecting a determined clearance between said first and second panels, to allow evacuation of zinc vapors.

Many examples of manufacturing processes of this type are known.

The assembly of galvanized sheet panels is usually made by laser welding by transparency. The lap weld and the weld in the radius, that is to say a weld made by a laser beam positioned between the radius of curvature of the first panel and the second panel, are difficult to implement because the important Dispersions of realization of the panels resulting from stamping only make it difficult to ensure satisfactory monitoring of the position of the laser beam.

Transparency welding gives excellent results in terms of holding the assembly made, but imposes high stresses in the welding of zinc-plated parts.

Indeed, it is necessary, during welding, to maintain the existence of a determined clearance of about 0.2 mm between the two panels to allow the zinc vapors to escape laterally from the weld bead and thus to less disturb the capillary discharge of the weld.

Also it is particularly difficult to perform this operation between an end portion of the first panel, parallel to the second panel, and said second panel, because the stamping tolerances are greater than the set of 0.2 mm sought.

The invention overcomes this disadvantage by assembling without play the end portion of the first panel and the second panel, and performing the operation of welding by transparency in the radius of curvature of the first panel, to achieve the welding according to the game determined.

For this purpose, the invention proposes a method of the type described above, characterized in that it comprises at least one prior step of setting in position during which the end portion of the first panel is superimposed without play on the second panel and in that during the laser welding step, the laser beam is positioned in an area of the radius of curvature of the first panel corresponding to the determined clearance between the first and second panels, a laser head delivering the laser beam being arranged on one side of the two panels to achieve a welding said "by transparency".

According to other characteristics of the method: during the laser welding step, the laser tip is arranged on the concavity side of the radius of curvature and is inclined at a determined angle according to which the beam passes through the center of the radius of curvature and the normal to the radius of curvature of the first panel, - during the laser welding step, the laser beam is arranged at a determined distance from the junction between the radius of curvature of the first panel and the second panel, which is associated with the realization of the weld in an area of the radius of curvature of the first panel corresponding to the set clearance between the first and second panels, - the method comprises a step of simultaneous joint tracking at the welding step laser, during which the position of the weld bead is continuously measured; - the method comprises a step of correcting the position of the laser head during which, as a function of the position of the weld bead measured during the seal tracking step, the position of the laser head is slaved to adjust the determined distance so as to enable the weld to be produced in the area of the first panel radius of curvature corresponding to the game determined between the first and second panels.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: FIG. 1 is a diagrammatic sectional view of an end of a hollow body, illustrating conventional welding processes. - Figure 2 is a schematic sectional view of one end of a hollow body, illustrating the welding process object of the invention. - Figure 3 is a schematic sectional view of one end of a hollow body, according to Figure 2, illustrating an exemplary resetting principle associated with the welding process object of the invention. In the following description, like reference numerals designate like parts or having similar functions. FIG. 1 shows the detail of a hollow body 10 of a motor vehicle.

In known manner, the hollow body 10 comprises at least a first panel 12 of sheet metal assembled to a second panel 14 of sheet metal. For example, the first panel 12 of sheet metal has at least one main portion 16 perpendicular to the second panel 14, an end portion 18 parallel to the second panel 14 and a defined radius of curvature 20 connecting said end portion 18 to the portion 16. In a known manner, several methods can be used to weld the first panel 12 to the second panel

14.

In the remainder of the present description, particular attention will be given to the welding operation of panels 12, 14 made of galvanized sheet metal, which require the maintenance of a determined clearance between the panels to be welded, to allow the evacuation of zinc vapors released by heating the panels, the evacuation of these vapors being imperative to prevent them from disturbing the capillary flow of the weld. As can be seen in FIG. 1, it is first possible to perform the "clap" welding in an end zone 22 of the first panel 12. However, this type of weld does not confer the best rigidity on the assembly.

It is also possible to perform the "transparent" welding in an Intermediate zone 24 of the end portion 18 of the first panel 12, a laser head delivering the laser beam being arranged on one side of the two panels 12, 14. this configuration, it is necessary, during the welding, to maintain the existence of a determined game (no shown) of about 0.2 mm between the two panels 12, 14 to allow the zinc vapors to escape laterally from the weld seam. it is therefore particularly difficult to perform this operation between the intermediate portion 24 of the first panel 12 and the second panel 14, because the stamping tolerances of the two panels 12, 14 are greater than the set of 0.2 mm sought.

Finally, it is possible to weld in an area 25 near the radius of curvature 20 of the first panel 12, but it is necessary to perform a precise positioning of the laser beam to achieve the realization of a weld bead between the radius of the curvature 20 of the first panel 12 and the second panel 14. The invention proposes to take advantage of the playable games between the radius of curvature 20 of the first panel 12 and the second panel 14 to perform a welding operation by transparency.

For this purpose, the invention proposes a method of welding panels 12, 14 described above, said method comprising at least one laser welding step in which the first panel is laser welded to the second panel respecting a set game between said first 12 and second panels 14, to allow the evacuation of zinc vapors.

According to the invention, as represented in FIG. 2, this method comprises at least one preliminary positioning step during which the end portion 18 of the first panel 12 is superimposed without play on the second panel 14. during the laser welding step, the laser beam 27 is positioned in a zone of the radius of curvature 20 of the first panel 12 corresponding to a set "J", typically of the order of 0.2 mm, between the first and second panels 12, 14. This configuration therefore makes it possible on the one hand to overcome the dimensional dispersions resulting from the stamping of the first and second panels 12, 14 and nevertheless to ensure compliance with the clearance "J" required for the evacuation of zinc vapors, Finally, the method according to the invention is advantageously characterized in that a laser head 26 delivering the laser beam is arranged on one side of the two panels 12, 14 to achieve a so-called "transparency" welding.

More particularly, the laser head 26 is preferably arranged on the concavity side of the radius of curvature.

This configuration has been shown in Figure 2.

The invention is advantageous in that the position of the laser head 26 in the horizontal direction "L" determines the clearance between the radius of curvature 20 of the first panel and the second panel 14 with which the weld is made.

It is therefore possible by varying the longitudinal position "X" of the laser head 26 measured from the junction between the radius of curvature 20 of the first panel 12 and the second panel 14, to vary the set "J". and reciprocally, that is to say to adjust the longitudinal position "X" of the laser head 26 to obtain a set "J" ideally corresponding to a value of 0.2mm.

A simple geometric relation makes it possible to calculate the theoretical position of the laser head 26. Indeed, as illustrated in FIG. 2, to obtain a clearance "J" on the outer radius "R" of the radius of curvature 20 from a position "X" of the laser head 26, we obtain the following relations: cos α = (RJ) / R and sin α = X / R from where: X = R sin [arccos ((RJ) / R)]

This calculation is obviously to be minored or increased according to the dimensioning dispersions obtained for the sheets considered. Thus, for example, for a standard sheet thickness 1.5mm, the inner radius of curvature "r" varying between 3mm and 6mm, which corresponds to an outer radius "R" varying between 4.5 and 6mm, for a clearance value "J" of between 0.17 mm and 0.23 mm, a theoretical positioning value "X" of the laser head of between 1.33 and 1.72 mm is obtained.

Another advantageous feature of the invention is that, preferably, the method includes a step of simultaneous seal tracking at the laser welding step, during which the position of the weld bead is continuously measured.

This measurement can also be performed to read the value of the rays made and thus recalculate the ideal positions of welding. This measurement is preferably optical.

In this way, the method may advantageously comprise a position correction step of the laser head 26 during which, depending on the position of the weld bead measured during the joint tracking step, the position of the weld bead is ensured. the laser head 26 to adjust the determined distance so as to allow the realization of the weld in the region of the radius of curvature 20 of the first panel 12 corresponding to the determined play "J" between the first and second panels 12, 14.

By way of example, the above correction step can be performed by means of a registration system, comprising, for example, a vision camera, a guide table associated with the laser head and a control unit. connected to the guide table and managed by different vision algorithms.

In particular, a first example of an algorithm used may be based on the principle of tracking a plane surface. The principle of this algorithm is to detect the end of the plane surface, which is built by linear interpolation from the left or the right (parameter to enter the algorithm). The tracking point is then set when the distance between the points in the part and the tracking line exceeds a value to be entered in the software. Another example of algorithm used is based on the principle of resetting from the detection of the two edges of the sheet, namely detection of the radiated part 20, and deduction of the center. Another example of an algorithm may be used in the case where the end portion 18 of the first panel 12 forms a step, as shown in FIG. 2, on the principle of taking this step into account during the resetting. The algorithm detects walking and uses the same principle as described above, namely the principle of tracking a flat surface.

Yet another example of an algorithm used may be based on the combination of the various principles described above, namely taking into account a step at the end portion of the first panel 12 and the use of an edge on the other side. This last example is illustrated very schematically in FIG. 3. The algorithm therefore takes into account the detection of the step at point A of FIG. 3 and determines the tracking point calculated from the radius at point B of FIG. This registration thus makes it possible to optimally adjust the position of the laser head 26, and therefore of the laser beam 27 (shown schematically by a solid line in FIG. 3) along the Y and Z axes.

The invention thus makes it possible to simply and effectively produce the assembly of hollow panels made of galvanized sheet metal by laser welding by transparency in the radius of curvature of a panel.

Claims

1. A method of manufacturing a hollow body (10) galvanized sheet for a motor vehicle, said hollow body having at least a first panel (12) of sheet assembled to a second panel (14) of sheet metal, said first panel ( 12) of sheet metal having at least one main portion (16) perpendicular to the second panel (14), an end portion (18) parallel to the second panel (14) and a defined radius of curvature (20) connecting said portion of end (18) to the main portion (16), said method comprising at least one laser welding step in which the first panel (12) is laser welded to the second panel (14) in a predetermined set (J) ) between the first and second panels (12, 14), to allow the evacuation of zinc vapors, characterized in that it comprises at least one preliminary step of setting in position during which the portion of end (18) of the first panel (12) on the cond panel (14) and in that during the laser welding step, the laser beam is positioned in an area of the radius of curvature (20) of the first panel (12) corresponding to the set (J) determined between the first and second panels (12, 14), a laser head (26) delivering the laser beam (27) being arranged on one side of the two panels (12, 14) to perform a so-called "transparency" welding. 2. Manufacturing method according to the preceding claim, characterized in that during the laser welding step, the laser head (26) is arranged on the concavity side of the radius (20) of curvature and is inclined a determined angle (α) according to which the beam passes through the center of the radius of curvature and the normal to the radius of curvature (20) of the first panel (12) 3. Manufacturing method according to the preceding claim, characterized in that during the laser welding step, the laser beam (27) is arranged at a determined distance (X) from the junction between the radius of curvature (20). ) of the first panel (12) and the second panel (14), which is associated with the realization of the weld in an area of the radius (20) of curvature of the first panel (12) corresponding to the game (J) determined between the first and second panels (12, 14). 4. Manufacturing process according to the preceding claim, characterized in that it comprises a simultaneous seal tracking step in the laser welding step, during which the position of the weld seam is continuously measured. The manufacturing method according to the preceding claim, characterized in that it comprises a step of position correction of the laser head (26) during which, depending on the position of the weld bead measured during the step With respect to joint tracking, the position of the laser head (26) is slaved to adjust the distance (X) determined so as to allow the welding to be carried out in the region of the radius of curvature (20) of the corresponding first panel (12). at the determined game between the first and second panels (12, 14).